feat(cas): complete Step 7 production render workspace

[shiuyu1124]

Summary

• Integrate ComfyUI video rendering provider
• Add CAS render request, task, view, and shot-render workflow
• Add production render workspace UI
• Add backend and frontend tests
• Complete Step 7 Production MVP implementation

Validation

• Backend tests passed
• Pylint passed (10/10)
• Frontend Vitest passed
• TypeScript check passed
• ESLint passed
• Vite production build passed

Next Step

Complete real ComfyUI Render Acceptance before merging and tagging.